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tr.v. pho·to·bombed, pho·to·bomb·ing, pho·to·bombs
1. To move unexpectedly and quickly into the frame of a photograph that is being taken of (someone or something): We were photobombed by my annoying cousin in half of our photos at the reception.
2. To appear unexpectedly in (a photograph), especially as a practical joke: My ridiculous roommate photobombed most of the pictures of me at the picnic.
A photograph in which a person, animal, or object appears unexpectedly along with or in front of the intended subject.
informal to intrude into the background of a photograph without the subject's knowledge
Past participle: photobombing